Piperazinones are useful compounds which are good absorbents for removing SO.sub.2 from gas streams. Piperazinones and substituted piperazinones are known and they can be prepared by several methods. N-alkyl- and N,N'-dialkylpiperazinones have been prepared by reacting an N-substituted alkylenediamine with a 2-oxoaldehyde which is disclosed in U.S. Pat. No. 4,767,860 and N-substituted hydroxyalkylpiperazinones have been prepared by the reaction of the appropriate piperazinone or of certain substituted piperazinones with an alkylene oxide or the analogous chlorohydrin. This reaction is described in U.S. Pat. No. 2,633,467 and in Chimie Therapeutique, May-June, 1969, No. 3, pp. 167--173. Recently issued U.S. Pat. No. 4,814,443 discloses a method of making these hydroxyalkyl-substituted compounds by reacting an .alpha.,.beta.-diketone, e.g. glyoxal, or an alkyl-substituted derivative of glyoxal, with an N-hydroxyalkylalkylenediamine.
An early process, described in U.S. Pat. No. 2,649,450, reacts an N,N'-dialkylethylenediamine with a carbonyl compound and HCN to obtain a 1,4-dialkyl-2-piperazinone. In an alternate process described in the same patent the amine was reacted with a ketone cyanohydrin. In U. S. Pat. No. 2,700,668, a process for making 2-piperazinone is described wherein ethylenediamine and glycolonitrile are reacted together.